High power electric motor and other control applications commonly utilize semiconductor bridge circuits for converting DC power to AC power, or vice versa. In an electric or hybrid vehicle, for example, a bridge circuit may be operated to power one or more AC drive motors from a DC storage battery, or alternately, to charge the DC storage battery from an AC source.
To simplify physical packaging of the bridge circuit, a pair of complementary bridge switches may be conveniently incorporated into a single module, sometimes referred to a dual switch module. In such a package, there are three current carrying terminals: a positive terminal, a negative terminal and a common terminal to which both bridge switches are connected.
An example of a dual switch module is shown in the U.S. Pat. No. 5,523,620 to Eytcheson et al., issued on Jun. 4, 1996, assigned to the assignee of the present invention, and incorporated herein by reference. In that module, a set of three current carrying terminals are arranged in linear fashion on a baseplate of the module, and the two complementary switches are formed by two sets of transistor subassemblies disposed on the baseplate on either side of the linearly arranged terminals. The terminals have integral frame portions that at least partially overlap to define two parallel rows of interdigitated connection areas, and each transistor subassembly is coupled to a pair of adjacent connection areas via metal foil tabs coupled to its respective transistor. The gate terminals of the various transistors are bonded to exposed tabs of a pair of metal lead frames insert molded into a housing of the module, and a pair of gate terminals provide electrical access to the lead frames. Due to the linear symmetry, this type of package is sometimes referred to as a parallel dual switch module.